Blubyu12

Well after many hours of diagnostic, the dealer found what was causing the check engine light/lean code was the auxiliary fuel pump. They replaced it but by low speed throttle response seems worse. From a stand still I have to be very careful how I apply the throttle, it's almost like a light switch ...off/on. It's really starting to get annoying and even dangerous. Was curious to know if there was supposed to have been some type of fuel system recalibration after the install of the fuel pump. I really don't want to take it back to the same dealer because I think we're about to go through some major issues problems as I attempt to collect my money back for the many hours of diagnostic that I was charged because they couldn't justify it to the warranty service.

PaulW

I wouldn't be surpirsed if the check engine light comes on again. Lean code because of the auxilary fuel pump?

I will have to check the Bently, but I don't think there is an auxiliary fuel pump.

Aarononymous

sounds like the suction jet pump which transfers fuel between the tank halves

PaulW

One on the right side of the tank, and one on the left side, the transfer pump.

I don't see how replacing the fuel transfer pump would have any effect on the code. However, it sure sounds like they hooked something up wrong....it should not be on/off when you hit the gas.

If that was the case, I would suspect the throttle position sensor....it does need to be recalibrated after certain replacements, like replacement of the MAF. You might want them to do that. It is: Throttle Position (TP) sensor -G79- and Sender 2 for accelerator pedal position -G185- In footwell on accelerator pedal (both senders are located in one housing)

Blubyu12

It was the fuel transfer pump that was replaced. It kicks in on start up and during heavy loads. When I put my foot in it, the motor was not getting enough fuel (bad pump) ie....lean code.

On another note, they did replace the MAF so i bet they didn't recalibrate.

The "on/off" feel is when I'm going very slow and just slightly touch the pedal, nothing happens, as I push down more, it kicks in....hard!!

I

PaulW

I just checked the wiring diagrams for both the fuel pump and the fuel transfer pump. The purpose of the fuel transfer pump is to transfer fuel from the left saddle in the tank to the right side where the fuel pump is.

It's powered from the +30 (12VDC) bus B146. This is the same bus that powers the O2 sensor heaters, so it's on when the car is on. It does not have a relay because it's a small pump. The main fuel pump has a relay that powers it.

The failure of this pump has nothing to do with a long term lean code. That's a dealer who is reaching for excuses.

Whoever repaired your car didn't get it right. If they replaced the MAF and it goes away, that is most likely your problem or unmetered air downstream of the MAF. That's what causes the code.

I would bring it back and tell them to get it right with the gas pedal. I did not see a TPS calibration procedure...<ul><li><a href="http://wiki.ross-tech.com/index.php/Throttle_Body_Alignment_(TBA)">Here is some info at ross-tech</a></li></ul>

Blubyu12

The new MAF didn't correct the problem, the new transfer pump did. Someone else on the site had the exact same problem. Thanks for the info. I'll be heading back to the dealer soon.

8Pack

I wrote this up for Blubyu before..but briefly, I had the EXACT same problem. All sorts of fixes were tried including replacing the MAF sensor and none worked, the CEL kept coming back on....

After 30 days at the dealer and calls to Germany through AOA, the discovered that the fuel transfer pump was not hooked up to the main pump. As explained to me by the tech and the head of service, the transfer pump does come "on" during heavy acceleration and acts as an auxiliary pump of sorts which if not working will cause a lean code to be thrown. Once the pump was hooked back up CEL never came back on, fixed miles ago and had been a problem since new 25......

I don't expect he will see the CEL with the same codes again now that the fuel transfer pump has been replaced...